This invention relates to a rotation transmission device mounted in the power train of an automobile for selectively transmitting the driving force.
While a four-wheel drive vehicle (4WD) is turning a tight corner of a paved road, the vehicle tends to behave as though brakes were applied unevenly. To prevent such "tight corner braking", the applicant of this invention proposed in Japanese patent application 8-172598 a rotation transmission device including a roller type two-way clutch and an electromagnetic clutch.
This rotation transmission device is mounted in an FR-based 4WD as shown in FIGS. 21 and 22. The 4WD shown includes a hub clutch 2 mounted at the base of each front wheel 1. The output of the engine 3 is transmitted through a transmission 4, an input shaft 6 in the transfer 5, and a rear propeller shaft 8 to rear vehicle wheels 7. The rotation transmission device is mounted in the transfer 5 and includes, as mentioned above, a roller type two-way clutch 9 for selectively transferring torque from the input shaft 6 to a front propeller shaft 13 for the front wheels 1, and an electromagnetic clutch 10 for selectively engaging and disengaging the two-way clutch 9. The rotation transmission device provides the vehicle with a 4WD control mode in addition to the ordinary 4WD travel modes (2WD, 4WD-Hi and 4WD-Lo).
Specifically, while the vehicle is traveling at a constant speed, this rotation transmission device transmits engine power to the rear wheels only (2WD). If one of the rear wheels begins to slip while the vehicle is being accelerated, an electric current is applied to the electromagnetic clutch 10 to lock the two-way clutch 9. The drive mode thus changes from 2WD to 4WD.
Similarly, if one or both rear wheels should slip due to sudden engine brake applied on a low-.mu. road, a current is applied to the electromagnetic clutch 10 to change the drive mode from 2WD to 4WD.
By selectively locking and unlocking the two-way clutch, the 4WD car can travel smoothly in any road condition.
With this rotation transmission device, the driver can freely select any of the 2WD mode, and 4WD LOCK mode, 4WD AUTO (control) mode as shown in FIG. 21. When the 2WD mode is selected, the hub clutches 2 of the front wheels are disengaged to stop the front drive train (hatched portion in FIG. 21). Fuel consumption can thus be saved.
This conventional rotation transmission device had one problem when the drive mode is changed from 2WD to 4WD LOCK or 4WD AUTO.
During 2WD, the hatched (FIG. 21) portion of the front drive train is at a stop while the vehicle is moving. To change the drive mode to 4WD in this state, i.e. while the vehicle is in motion, the only way is to lock the two-way clutch 9. However, if the two-way clutch 9 were locked in this state, a large shock would be inflicted on the vehicle, so that the two-way clutch 9 and other parts in the power train would be damaged, because the nonrotating parts are suddenly coupled to the rotating parts through the clutch 9.
Conventional rotation transmission devices are therefore practically incapable of changing from 2WD to 4WD mode while the vehicle is in motion. For this purpose, the vehicle has to be stopped first.
An object of this invention is to provide a rotation transmission device with a synchronizing function that permits a smooth mode change from 2WD to 4WD even while the vehicle is moving.